You'd want to ship the yellowcake as HAZMAT Class 7 radioactive and it cannot be shipped outside the United States without an NRC export license (probably continental US only too).

The hydrofluoric acid should be shipped as HAZMAT Class 8 corrosive.

Edit: If you're asking why it's legal to sell this stuff, naturally occurring uranium is over 99% U238 isotopes. Extracting useful U235 from it requires some really nasty chemistry, insane amounts of electricity, and very specialized hardware like gaseous centrifuges powerful enough to separate isotopes. Buying the thousands of kilograms you'd need to build a bomb would set off a ton of alarm bells all up and down every major government but small samples for educational or novelty purposes aren't a concern.